Bodily tissue dilation systems and methods

ABSTRACT

A dilating system for dilating bodily tissue includes a elongate tubular first dilator and a elongate tubular second dilator. The second dilator has an outer diameter greater than the outer diameter of the first dilator, the first dilator being configured to be received within the second dilator. In one embodiment, a first mating member is formed on the exterior surface of the first dilator while a second mating member is formed on the interior surface of the second dilator. The first mating member engages with the second mating member when the second dilator is passed over the first dilator so as to cause the second dilator to travel along a fixed path relative to the first dilator.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

This invention is in the field of apparatus and methods for dilatingbodily tissue in order to provide surgical access to a desired area ofthe body, such as for providing surgical access to the spine.

2. The Relevant Technology

Dilation systems are employed to move the skin, muscle, and other bodilytissues away from a surgical site in order to provide a surgeon accessto bone or other bodily tissue where surgery is required. In a spinalsurgery, for example, it is often desired to separate the skin and othertissue away from a particular desired surgical site prior to surgery. Inorder to perform this function, the skin and other tissue may be pulledaway from the insertion site and a retractor placed in the insertionsite to retain the skin and other tissue away from the surgical siteduring the surgical procedure.

One example of a dilation system that is employed during such a surgeryis a dilation system having a plurality of tubular members that can beconcentrically disposed. Each tubular member has a uniformly smoothinterior surface and exterior surface. Initially, a guide wire isinserted within a small incision formed at the surgical site. Next, asmallest first tubular member is feed over the guide wire so that adistal end of the first tubular member is advanced into the surgicalsite. As the distal end advances into the incision, the tissuesurrounding the first tubular member is radially outwardly retracted ordilated.

Once the first tubular member is inserted to a desired depth, a slightlylarger second tubular member is pushed over the second tubular memberand into the tissue so as to further dilate the tissue. This process isrepeated for additionally larger tubular members until the tissue at thesurgical site is retracted to a desired extent to facilitate thesurgical procedure.

Although conventional dilation systems function to retract the tissue,they have a number of shortcomings. For example, it is often desirableto have each subsequent tubular member penetrate to the same depth inthe tissue as the first tubular member. In conventional systems,however, it is difficult to know the exact depth that each tubularmember is inserted. Furthermore, conventional tubular member are simplypushed into the tissue. Because of applied friction forces produced bythe tissue, it is often difficult to advance each tubular member to adesired depth without over penetrating. That is, as static frictionforces are initially overcome, the pushing force applied to a tubularmember can cause the tubular member to advance too far into the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of a dilation system of the presentinvention with the dilators shown in a nested, telescoping assembly.

FIG. 2 is an exploded view of the dilation system of FIG. 1 with thebroken lines demonstrating the sequential advancement of a dilator ofthe system along a guide wire, followed by larger dilators beingadvanced sequentially along the initial dilator and each other, followedby a tubular retractor being advanced along the largest dilator of thesystem.

FIG. 3 is a cross sectional view of the dilation system of FIG. 1.

FIG. 3 a is an enlarged view of the distal insertion ends of thedilators shown in FIG. 3.

FIG. 4 is a perspective view of the tubular retractor of the dilationsystem of FIGS. 1 and 2.

FIG. 5 is a cross-sectional view of the retractor of FIGS. 1, 2 and 4.

FIG. 6A is a cross-sectional schematic view demonstrating the insertionof a guide wire through the tissue of a patient into a desired surgicalsite.

FIG. 6B demonstrates a first dilator being placed over the guide wire ofFIG. 6A and guided down to the surgical site creating an initialinsertion corridor through which a surgical procedure can be performed.

FIG. 6C demonstrates the advancement of a second dilator along the firstdilator such that internal mating members of the second dilator engagethe external mating members of the first dilator, thereby following andenlarging the initial insertion corridor.

FIG. 6D demonstrates the second dilator having reached the surgicalsite, as demonstrated by the release of the internal mating members ofthe second dilator from the external mating members of the first dilatorsuch that the second dilator rotates freely about the tapered portion ofa first dilator.

FIG. 6E demonstrates the advancement of a third dilator over the seconddilator after the first dilator has been removed from within the seconddilator.

FIG. 6F demonstrates the third dilator having reached the surgical site.

FIG. 6G demonstrates the advancement of a fourth dilator over the thirddilator after the second dilator has been removed from within the thirddilator.

FIG. 6H demonstrates the advancement of a fifth dilator over the fourthdilator after the third dilator has been removed from within the fourthdilator.

FIG. 6I demonstrates the advancement of a sixth dilator over the fifthdilator while the fourth dilator remains within the fifth dilator.

FIG. 6J demonstrates the advancement of a tubular retractor over thesixth dilator.

FIG. 6K demonstrates the retractor having reached the surgical site, asdemonstrated by the release of the internal mating members of theretractor from the external mating members of the sixth dilator suchthat the retractor rotates freely about the tapered portion of a sixthdilator.

FIG. 6L demonstrates the retractor having reached the surgical site andthe sixth dilator having been removed therefrom such that a surgicalinstrument can be advanced through the retractor.

FIGS. 7-9A are cross sectional side views of alternative embodiments ofinternal and external mating members that can be used on dilators.

FIGS. 9B-9D are elevated side views of the exterior surface of the innerdilator shown in FIG. 9A having different track configurations thatfunction as mating members.

FIG. 10 is a partial cross sectional side view of an inner and outerdilator having tissue engaging members formed thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an example of a dilation system 10 for dilating bodily tissue.System 10 comprises (i) a guide wire 20 that is inserted to a surgicalsite; (ii) a plurality of concentric sequentially larger dilators 30,60, 90, 110, 130, 150 (shown as being nested in FIG. 1) that aresequentially introduced into bodily tissue over the guide wire; and(iii) a retractor 160 that is introduced over the largest introduceddilator 150.

After guide wire 20 is inserted to a desired depth within the tissue ofa surgical site, first dilator 30 is passed over guide wire 20 and intothe tissue. First dilator 30 circumferentially stretches or dilates thebodily tissue a certain distance, thereby forming an initial insertioncorridor. The larger diameter dilators are then sequentially passed overfirst dilator 30 so as to further dilate the bodily tissue and form asequentially larger insertion corridor at the surgical site.

Once the largest diameter dilator 150 has been introduced, the retractor160 is introduced over the dilator 150, thereby establishing the finaldiameter of the insertion corridor and maintaining the insertioncorridor during a surgical procedure. Following removal of the guidewire 20 and dilators 30-150, surgical devices and instruments can beinserted through the retractor 150 to the surgical site.

In one embodiment of the present invention, in order to avoidover-penetration of the surgical site, the dilators 30-150 and retractor160 have complementary mating members on select interior and exteriorsurfaces. More specifically, dilators 30-150 feature one or more threadsdisposed on the exterior surface at a distal end of each dilator. One ormore tangs project from the interior surface of dilators 60-150. As alarger dilator is advanced over a smaller dilator, the tang(s) engagewith the thread(s) so as to force the larger dilator to travel along afixed path relative to the smaller dilator. In one embodiment, theexterior surface at the distal end of each dilator radially inwardlytapers. The taper is configured such that the tang(s) disengage from thethread(s) when the larger dilator is inserted to the desired depth. Thusa surgeon is able to both visually see and tactilely feel when eachdilator is inserted to a desired depth.

The components of the guide wire 20 and dilators 30-150 and theirinteraction will now be described in additional detail with reference toFIGS. 2-3A. The retractor 160 will then be described in additionaldetail in FIGS. 4-5 and a method for dilating tissue using system 10will then be described with reference to FIGS. 6-6L. Additionalalternative embodiments will then be discussed with reference to FIGS.7-10.

With reference now to FIGS. 2-3 a, guide wire 20 has a proximal end 22and a distal insertion end 24 that terminates at a distal tip 26. Guidewire 20 can comprise any conventional guide wire. Once guide wire 20 isinserted into a desire surgical site on the body, first dilator 30 isreceived over proximal end 22 of guide wire 20 and advanced along guidewire 20.

Dilator 30 comprises an elongated tubular body 32 having an exteriorsurface 44 and an interior surface 45 each extending between a proximalend 34 and an opposing distal insertion end 36. Interior surface 45bounds a passageway 43 having a proximal opening 38 at the proximal end34 and a distal opening 40 at the distal end 36. Passageway 46 isconfigured to allow guide wire 20 to pass therethrough. The exteriorsurface 44 includes a tapering portion 48 that constricts towards andterminates at a distal terminus 46. In other words, the distal insertionend 36 of tubular body 32 has a tapering portion 48 that decreases indiameter toward distal terminus 46. Tapering portion has a substantiallyfrustoconical configuration. Dilator 30, as with the other dilators, canbe made of any material such as metal, plastic, or composite and can beradiopaque or radiolucent.

Dilator 30 further comprises an external mating member outwardlyprojecting from exterior surface 44 of tubular body 32 at distalinsertion end 36. In the embodiment depicted, the external mating membercomprises an external thread 50 helically extending around tubular body32 on exterior surface 44. Thread 50 is formed on tapering portion 48and extends to distal terminus 46. In one alternative, thread 50 cancomprise two or more discrete threads.

Similar to first dilator 30, second dilator 60 comprises an elongatedtubular body 62 having an exterior surface 72 and an interior surface 74each extending between a proximal end 64 and an opposing distalinsertion end 66. Interior surface 74 bounds a passageway 71 having aproximal opening 68 at the proximal end 64 and a distal opening 70 atthe distal insertion end 66. Passageway 71 of second dilator 60 isconfigured to receive first dilator 30. Second dilator 60 also has atapering portion 84 located at distal insertion end 66 that decreases indiameter toward and terminates at a distal terminus 82.

As further shown, second dilator 60 has an external mating memberoutwardly projecting from exterior surface 72 and an internal matingmember projecting from interior surface 74 of tubular body 62 each atdistal insertion end 66. Specifically, the external mating membercomprises one or more threads 76 formed on exterior surface 72 and theinternal mating member comprises first and second tangs 78 a-bprojecting on the interior surface 74 at or adjacent to distal terminus82.

Tangs 78 a-b of second dilator 60 are configured to threadedly mate withthread 50 of first dilator 30 when second dilator 60 is advanced overfirst dilator 30, as shown in FIGS. 3 and 3A. In this regard, thread 50forms bounded tracks that receive and guide tangs 78 a-b. Specifically,once proximal end 34 of first dilator 30 is received within distalinsertion end 66 of second dilator 60, second dilator 60 can be freelyadvanced over first dilator 30 until tangs 78 a-b reach thread 50.Further advancement of second dilator 60 requires selective rotation ofsecond dilator 60 relative to first dilator so that tangs 78 a-b engagewith and advance along thread 50. During the engagement between tangs 78a-b and thread 50, second dilator 60 is forced to travel along a fixedpath that prevents free rotation of second dilator 60 relative to firstdilator 30. That is, second dilator 60 can only rotate along the fixedpath. It is noted that second dilator 60 has a length that is shorterthan first dilator 30. This variance in length enables first dilator 30to be held stationary by the surgeon holding onto the exposed proximalend 34 of first dilator 30 while second dilator 30 is advanced androtated.

As tangs 78 a-b are threaded downwardly along external thread 50, thetangs 78 a-b reach the tapered portion 48 of first dilator 30. Taperedportion 48 is configured such that at the point when distal terminus 82of second dilator 60 is aligned with distal terminus 46 of first dilator30, tangs 78 a-b disengage from thread 50 due to the constriction oftapered portion 48. As a result of tangs 78 a-b disengaging from thread50, second dilator 60 is again free to rotate relative to first dilator30. Upon feeling the free rotation, the surgeon knows that the seconddilator 60 is at the same depth as first dilator 30 and thus can stopfurther advancement into the tissue, thereby preventing over-penetrationof second dilator 60. In other embodiments, tangs 78 a-b and thread 50can be set so that second dilator 60 disengages from first dilator 30 atany desired relative position relative to first dilator 30.

Once dilator 60 has been inserted to the desired position, additionaldilators can added. Dilators 90, 110, 130, and 150 similarlysequentially increase in diameter and decrease in length. Each of thedilators also has an external mating member, i.e., one or more outwardlyprojecting threads, and an internal mating member, i.e., one or moreinwardly projecting tangs. Each of the dilators also includes a taperingportion on which the external threads extend. In view of the increasingdiameter size of the dilators, an increasingly larger dilator insertioncorridor is formed by sequentially passing larger dilators over smallerdilators.

For example, third dilator 90 comprises a third tubular body 92 thatbounds a passageway 93. Third tubular body 92 has a diameter that islarger than the diameter of second tubular body 62. An external thread94 and interior tangs 96 a-d are formed at a distal insertion end 98 ofthird tubular body 92. Similarly, the fourth, fifth and sixth dilators110, 130, 150 have respective tubular bodies 112, 132, 152 each boundinga passageway extending between a proximal end and an opposing distalinsertion end 118, 138, and 158, respectively. External threads 114,134, 154 and internal tangs 116 a-d, 136 a-d, 156 a-d are formed ondistal insertion ends 118, 138, and 158 of dilators 110, 130, 150,respectively.

As indicated, each of the sequentially larger dilators 110, 130, 150also has a tapered distal portion at the distal insertion end thereof.As a result, the internal mating members of each larger dilator areconfigured to engage with external mating members of the next smallerdilator received therein. The larger dilator disengages from the smallerdilator when the distal terminus of the larger dilator aligns with thedistal terminus of the smaller dilator.

In addition, the tubular retractor 160, as will be discussed below ingreater detail, is designed to spin freely about the final dilator 150when the retractor 160 is placed thereabout and threaded along thedistal insertion end 158 thereof.

FIGS. 3 and 3A show a nested mating relationship of the dilators 30-150,with the dilator 30 over the guide wire 20 and with the retractor 160being shown over the dilator 150. As shown in these views, the internaltangs 78 a and 78 b can be threaded along exterior thread 50 of dilator30 and the internal tangs of the subsequently larger dilators can matewith exterior threads of respective dilators.

FIGS. 3 and 3A illustrate the interlocking features of the variousdilators and their possible relationship with respect to each other.FIGS. 1, 3 and 3A also illustrate how the guide wire 20, dilators30-150, and retractor 160 can be conveniently stored prior to use, forexample. During a surgical procedure, once dilator 30 is placed overguide wire 20, guide wire 20 may be removed or retained as otherdilators are applied. Similarly, dilator 30 may be removed or retainedfrom within dilator 60 once dilator 60 is passed over dilator 30, as canthe other dilators once the larger dilators are passed over them.

Retractor 160 will now be described in additional detail with referenceto FIGS. 2-5. Retractor 160 comprises a tubular body 161 having aproximal end 162 and an opposing distal insertion end 164. A proximalopening 166 is formed at the proximal end 162 and a distal opening 168is formed at the distal end 164. Body 161 also has an exterior surface170 and an interior surface 172, each extending from the proximal end162 to the distal insertion end 164. As shown, mounted on the interiorsurface at the distal insertion end 164 thereof are a plurality ofinternal mating members. Specifically, tangs 174 a-d are formed oninterior surface 172 so as to mate with the external thread 154 of thelast dilator 150. As with other dilators, tangs 174 a-d of retractor 160are designed to disengage from thread 154 when the distal terminus 175of retractor 160 is aligned with the distal terminus of dilator 150.

Retractor 160 is also shown in FIG. 5 in a cross-sectional view. Asshown in FIGS. 4 and 5, tangs 174 a-d comprise a small tab or other formof projection that extends inwardly from the interior surface 172 oftubular body 161 so as to engage the thread on dilator 150. Optionally,the mating member or members may comprise one or more threads. In yetother embodiments, retractor 160 can be free of mating members on itsinterior surface. In this embodiment, retractor 160 does notmechanically engage with dilator 150.

Extending about tubular body 161 is an annular rim 180. Rim 180 has aconnecting arm 182 extending therefrom. The connecting arm 182 has anintermediate notch 184 and a peripheral notch 186. A surgicalinstrument, e.g., equipment, tools, or supplies, may be coupled to theconnecting arm 182 for use during surgery or may be coupled to theconnecting arm 182 in order to stabilize the retractor and prevent itfrom moving during the surgery. The notches are configured to receive orotherwise couple to such instruments. For example, in one embodiment astabilizing arm is connected to one or more notches in order tostabilize the retractor 160 in a desired position during a surgicalprocedure. The rim 180 may rest on the skin surrounding the periphery ofthe insertion corridor during surgery, for example. Arm 182 is thuslinked to the tubular body 161 of the retractor. The arm 182 may belinked to the tubular body 161 by being indirectly coupled thereto or bybeing coupled directly thereto.

With reference now to FIGS. 6 a-6 k, a method for dilating bodily tissuewill now be discussed. As shown in FIG. 6 a, in one embodiment a guidewire 20 is first passed through bodily tissue 200 such as skin 202 andmuscle 204 until a portion of bone 206, e.g., a vertebrae, or anothersurgical site is contacted. In another embodiment, the guide wire 20 ispassed through bodily tissue without contacting bone. The guide wire 20may be inserted through a small incision, e.g., a 10-15 mm incision.

Next, as shown in FIG. 6 b, first dilator 30 is advanced over guide wire20 and into the tissue until the distal terminus 46 of first dilator 30contacts the surgical site. The external thread 50 of dilator 30 may beused in a cutting or corkscrew fashion to dilate the bodily tissue byrotating dilator 30 as dilator 30 is advanced into the insertioncorridor along guide wire 20. External thread 50 thus helps to controlthe advancement of dilator 30 into the tissue as dilator is rotated. Asshown, upon advancing the first dilator over the guide wire 20 a desireddistance, the tissue 200 begins to separate, forming an insertioncorridor 208 in the bodily tissue 200. As will be illustrated in thenext figures, the insertion corridor 208 increases as the diameter ofthe dilator therein increases.

Once the distal insertion end 36 of the first dilator 30 is advanced toa desired location, the guide wire 20 can then be removed from withinthe first dilator 30. Optionally, the guide wire 20 can be allowed toremain within first dilator 30 and can be removed once the retractor 160has been placed within the insertion corridor 208. As another option, itis possible to insert first dilator 30 into bodily tissue and beginformation of an insertion corridor without initially employing a guidewire to begin the insertion corridor.

FIG. 6C demonstrates the placement of second dilator 60 over firstdilator 30. The Figure illustrates that the internal tangs 78 a-b ofsecond dilator 60 engage the thread of first dilator 30 so as to therebyselectively thread downwardly into the insertion corridor 208 formed byfirst dilator 30. Once the sequentially larger diameter dilator (e.g.,dilator 60) is passed over the smaller diameter dilator (e.g., dilator30), the surgeon can hold the smaller diameter dilator 30 in place bygrasping the exposed proximal end of the dilator 30.

As shown in FIG. 6D, once tangs 78 a-b of second dilator 60 are movedadjacent the tapering portion 48 of first dilator 30, tangs 78 a-bdisengage from thread 50 on the exterior surface of dilator 30. Thisenables tangs 78 a-b and thus second dilator 60 to freely rotate ineither direction with respect to first dilator 30. As previouslymentioned, tangs 78 a-b disengage from thread 50 when the distalterminus of second dilator 60 is aligned with the distal terminus offirst dilator 30. Accordingly, the ability to freely rotate the seconddilator 60 relative to the first dilator 30 signals to the practitionerthat the surgical site has been reached, as shown in FIG. 6D. Thepractitioner can then stop advancing the second dilator 60 and thusprevent over-penetration of the second dilator 60 into the surgicalsite. Once second dilator 60 has reached the surgical site of FIG. 6D,the first dilator 30 can then be removed from within the second dilator60 or be allowed to remain therein. Also as shown in FIG. 6D, the distalinsertion end of the second dilator 60 is disengaged from, but continuesto surround the distal insertion end of the first dilator 30.

FIGS. 6E-6I demonstrate the placement of subsequently larger dilators90-150 into insertion corridor 208 by threading dilator 90 over dilator60 and threading subsequently larger dilators over dilator 90. Theprogressively larger dilators are threaded over the previous dilatoruntil the insertion corridor is dilated to the desired diameter. FIG. 6Edemonstrates the advancement of third dilator 90 along the thread 76 ofsecond dilator 60. FIG. 6F demonstrates that third dilator 90 hasreached the surgical site, has dilated the insertion corridor 208 andcan freely rotate with respect to second dilator 60.

FIG. 6G demonstrates the placement of fourth dilator 110 over thirddilator 90 (following the removal of dilator 60 from within dilator 90).FIG. 6H demonstrates the placement of fifth dilator 130 over fourthdilator 110 (following the removal of third dilator 90 from withinfourth dilator 110). FIG. 6I demonstrates the placement of thesequentially largest sixth dilator 150 over fifth dilator 130 whilefourth dilator 110 is still located within fifth dilator130—illustrating that the subsequently larger dilator may optionally beplaced over a dilator while another smaller dilator is still therein.

FIG. 6J demonstrates the placement of retractor 160 over dilator 150.FIG. 6K illustrates the movement of retractor 160 to the surgical site,threading over dilator 150. Once all the dilators, including dilator 150have been removed, tubular retractor 160 remains in the surgical site,retracting the bodily tissue and retaining the insertion corridor 208during a surgical procedure.

As reflected in FIG. 2 and previously mentioned, as the diameters of thesequential dilators 30, 60, 90, 110, 130, 150 increase, the lengths ofthe sequential dilators decrease. Thus, first dilator 30 is longer thansecond dilator 60, which is longer than third dilator 90, and so on. Thedecreasing length of the sequentially increasing diameter dilatorsenables the smaller diameter dilators to be held in position while alarger diameter dilator is advanced thereover. It also enables a smallerdiameter dilator to be removed while a larger diameter dilator is heldin place.

In order for the larger diameter dilator to freely rotate with respectto the smaller diameter dilator, the interior mating members must beshort enough that they do not engage the exterior thread of the smallerdilator when moved adjacent a tapered portion. The tangs disclosed inFIGS. 2-5, for example, are sufficiently short that they can engage theexterior thread until reaching the tapered portion wherein the tangsdisengage from the threads. In contrast or conjunction to tapering thebodies of the dilators, the distal ends of the threads can taper towardthe distal end or can terminate prior to the distal terminus of thedilators. In either embodiment, the tangs can disengage from the threadswhen the distal terminus are aligned.

In one embodiment of the present invention, means are provided forforcing a second dilator to travel along a substantially fixed path thatprevents free rotation of second dilator relative to a first dilatorwhile at least a portion of the second dilator is being advanced overthe first dilator. By way of example and not by limitation, oneembodiment of the recited means corresponds to the external threads,such as threads 50, 76, and 94, and the corresponding internal tangswhich engage with the external threads, such as tangs 78, 96, and 116,as described above. It is appreciated, however, that there are a varietyof alternative embodiments which can be used to accomplish the samefunction. For example, any number of complementary tangs and threads canbe used in a given embodiment. Furthermore, the tangs can be replacedwith any form of projection that engages with the threads. In yetanother embodiment, the tangs and threads need not be located at thedistal insertion end of the first and second dilator. Rather, the tangsand threads can be located at any complementary location along thedilators. For example, if the threads and tangs are disposed along acentral section of the dilators, the tangs can be positioned todisengage from, i.e., move distally past, the threads at the point wherethe distal terminus of the second dilator is aligned with the distalterminus of the first dilator. In this embodiment the threads need notbe on a tapered portion.

In yet another embodiment, the tangs and threads can be reversed. Forexample, as depicted in FIG. 7, a tang 220 is mounted on an exteriorsurface of an inner dilator 222 while a thread 224 is helically formedon an interior surface of an outer dilator 226. Again, tang 220 ispositioned relative to thread 224 such that when a distal terminus 228of outer dilator 226 is aligned with a distal terminus 230 of innerdilator 222, tang 220 disengages from thread 224 so that outer dilator226 can freely rotate about inner dilator 222.

In still another embodiment as depicted in FIG. 8, one or more threads232 can be formed on the exterior surface of inner dilator 222 while oneor more complementary threads 234 can be formed on the interior surfaceof outer dilator 226. The engagement between threads 232 and 234 causesouter dilator 226 to move in a fixed path relative to inner dilator 222.In the embodiment depicted, outer dilator 226 cannot freely rotaterelative to inner dilator 222 when distal terminuses 228 and 230 arealigned due to the continued engagement between threads 232 and 234.Although not required, in the depicted embodiment a marking 238 isformed on the exterior surface of inner dilator 222. Marking 238 ispositioned to align with a proximal terminus 238 of outer dilator 226when distal terminuses 228 and 230 are aligned. This again helps thesurgeon ensure that outer dilator 226 does not over-penetrate thesurgical site. It is also appreciated that by forming the threads 232and 234 proximal, the threads can be aligned to disengage when distalterminuses 228 and 230 are aligned. It is further appreciated that thethreads and other various mating members can be formed along the entirelength of one or both of the dilators.

In yet another embodiment as depicted in FIG. 9A, a mating membercomprises a track 240 formed along the exterior surface of inner dilator222. Tang 220 projects from the interior surface of outer dilator 226and is configured to be received within track 240. As a result, outerdilator 226 is forced to travel along a fixed path relative to innerdilator 222. Track 240 can be any desired configuration. For example, inFIG. 9B track 240 has a sinusoidal configuration while in FIG. 9C track240 is linear. In FIG. 9D, track 240 is helical. Although not required,depicted in FIG. 9A track 240 ends at a tapered section such that tang220 disengages from track 240 when distal terminus 228 and 230 arealigned. Outer dilator 226 is thus free to rotate relative inner dilator222.

In still other embodiments it is again appreciated that track 240 andtang 220 can be switched between the interior and exterior surfaces.Various tracks can also be formed by outwardly projecting threads, as inFIG. 7, or by rails or other projecting members. In view of theforegoing, it is appreciated that there is a wide variety of differenttype, configures, size and numbers of mating members that can be used tocomplementary mate so that a second dilator is caused to travel along asubstantially fixed path that prevents free rotation of second dilatorrelative to a first dilator while at least a portion of the seconddilator is being advanced over the first dilator.

Although FIGS. 7-9 only show mating members on the interior surface ofouter dilator 226 and the exterior surface of inner dilator 222, it isalso appreciated that mating members can be formed on the exteriorsurface of outer dilator 226 and the interior surface of inner dilator222 so as to further mate with other dilators or retractors.

The present invention also provides tissue engaging members. The tissueengaging members enable smooth and controlled advancement of thedilators into the body tissue. For example, depicted in FIG. 10 is innerdilator 222 having sloped thread portions 244 formed on the exteriorsurface adjacent to distal terminus 230. Thread portions 244 functionlike a drill bit or auger to help advance inner dilator 222 in acontrolled manner into the body tissue as second dilator 222 isselectively rotated. This controlled advancement helps to eliminateover-penetration caused by pushing on conventional dilators. In likemanner, thread portions 244 are also formed on the exterior surface ofouter dilator 226. In alternative embodiments the tissue engagingmembers can comprise helical threads, blades, or any other type ofprotrusion of groove that assists the dilator in controlled advancementinto the bodily tissue as the dilator is rotated.

Although tissue engaging members can have the same configuration asmating members, thread portions 244 are not referenced in FIG. 10 as amating member because there is no complementary mating member on theinterior surface of outer dilator 226 for thread portions 244 to engage.In another embodiment, separate mating members can be formed on dilators222 and 226 proximal of thread portions 244. In yet other embodiments astructural feature may function as both a mating member and a tissueengaging member. For example, threads 50, 76, 94 in FIG. 2 function asboth a mating member and a tissue engaging member.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A dilation system for dilating bodily tissue, the dilation systemcomprising: an elongate first dilator comprising a tubular body havingan exterior surface extending between a proximal end and an opposingdistal insertion end, the body also having an interior surface boundinga passageway extending between the proximal end and the distal insertionend; a first mating member formed on the exterior surface of the firstdilator at the distal insertion end; and an elongate second dilatorcomprising a tubular body having an exterior surface extending between aproximal end and an opposing distal insertion end, the body also havingan interior surface bounding a passageway extending between the proximalend and the distal insertion end, the passageway of the second dilatorbeing configured to receive the tubular body of the first dilator, thesecond dilator mechanically engaging with the first mating member suchthat the second dilator is forced to travel along a fixed path thatprevents free rotation of the second dilator relative to the firstdilator while at least a portion of the second dilator is being advancedover the first dilator, wherein the distal insertion end of the firstdilator and the second dilator each terminate at a distal terminus, thesecond dilator mechanically disengaging from the first dilator when thedistal terminus of the second dilator is at least substantially alignedwith the distal terminus of the first dilator such that the seconddilator is free to rotate about the first dilator.
 2. A dilation systemas recited in claim 1, further comprising: a second mating member formedon the interior surface of the second dilator, the second mating memberbeing configured to engage with the first mating member when the firstdilator is received within the passageway of the second dilator.
 3. Adilation system as recited in claim 1, wherein the first mating membercomprises an outward projecting member or a bounded track.
 4. A dilationsystem as recited in claim 3, wherein the outward projecting membercomprises a thread, thread portion, or tang.
 5. A dilation system asrecited in claim 2, wherein the second mating member comprises aprojecting member or a bounded track.
 6. A dilation system as recited inclaim 1, wherein the distal insertion end of the first dilator has atapered frustoconical configuration.
 7. A dilation system as recited inclaim 1, further comprising a third mating member formed on the exteriorsurface of the second dilator.
 8. A dilation system as recited in claim1, wherein the first dilator has a length and the second dilator has alength that is shorter than the length of the first dilator.
 9. Adilation system for dilating bodily tissue, the dilation systemcomprising: an elongate first dilator comprising a tubular body havingan exterior surface extending between a proximal end and an opposingdistal insertion end, the body also having an interior surface boundinga passageway extending between the proximal end and the distal insertionend; an elongate second dilator comprising a tubular body having anexterior surface extending between a proximal end and an opposing distalinsertion end, the body also having an interior surface bounding apassageway extending between the proximal end and the distal insertionend, the passageway of the second dilator being configured to receivethe tubular body of the first dilator; and means located at the distalinsertion ends of the first and second dilators for forcing the seconddilator to travel along a substantially fixed path that prevents freerotation of second dilator relative to the first dilator while at leasta portion of the second dilator is being advanced over the firstdilator, wherein the distal insertion end of the first dilator and thesecond dilator each terminate at a distal terminus, the second dilatorbeing free to rotate about the first dilator when the distal terminus ofthe second dilator is at least substantially aligned with the distalterminus of the first dilator.
 10. A dilation system as recited in claim9, wherein the means for forcing the second dilator to travel along asubstantially fixed path comprises: a first mating member formed on theexterior surface of the first dilator; and a second mating member formedon the interior surface of the second dilator, the second mating memberbeing configured to engage with the first mating member when the firstdilator is received within the passageway of the second dilator.
 11. Adilation system as recited in claim 10, wherein: the first mating membercomprises at least one first thread outwardly projecting on the exteriorsurface of the first dilator; and the second mating member comprises atleast one tang or at least one second thread inwardly projecting fromthe interior surface of the second dilator.
 12. A dilation system asrecited in claim 10, wherein at least a portion of the exterior surfaceof the first dilator on which the first mating member is formed istapered.
 13. A dilation system as recited in claim 10, furthercomprising a third mating member formed on the exterior surface of thesecond dilator.
 14. A dilation system as recited in claim 9, wherein thefirst dilator has a length and the second dilator has a length that isshorter than the length of the first dilator.
 15. A dilation system asrecited in claim 9, further comprising a guide wire, the passageway ofthe first dilator being configured to receive the guide wire.
 16. Adilation system for dilating bodily tissue, the dilation systemcomprising: an elongate first dilator comprising a first tubular bodyhaving an exterior surface extending between a proximal end and anopposing distal insertion end, a first mating member formed on theexterior surface of the first tubular body at the distal insertion end,the first mating member terminating at a distal terminus; and anelongate second dilator comprising a second tubular body having aninterior surface and an exterior surface, the interior surface boundinga passageway extending between a proximal end and an opposing distalinsertion end, the passageway of the second tubular body beingconfigured to receive the first tubular body, a second mating membercomprising a projecting tang being formed on the interior surface of thesecond tubular body, the second mating member engaging with the firstmating member when the first dilator is received within the passagewayof the second dilator, wherein the second dilator travels along asubstantially fixed path relative to the first dilator as a portion ofthe first dilator is advanced within the passageway of the seconddilator and the first mating member engages the second mating member,and wherein the second dilator freely rotates about the first dilatorwhen the first dilator is received within the passageway of the seconddilator and the second mating member is at least substantially alignedwith the distal terminus of the first mating member.
 17. A dilationsystem as recited in claim 16, wherein the first mating member comprisesa track that is at least partially bounded.
 18. A dilation system asrecited in claim 17, wherein the track is curved or linear.
 19. Adilation system as recited in claim 16, wherein the first mating membercomprises a thread, thread portion, or tang.
 20. A dilation system asrecited in claim 16, further comprising an elongate third dilatorcomprising a third tubular body having an interior surface and anexterior surface, the interior surface bounding a passageway extendingbetween a proximal end and an opposing distal insertion end, thepassageway of the third tubular body being configured to receive thesecond tubular body.
 21. A method for dilating bodily tissue, the methodcomprising: dilating bodily tissue with a distal insertion end of afirst dilator; positioning a proximal end of the first dilator within apassageway of a tubular second dilator; advancing the second dilatorover the first dilator; mechanically engaging the second dilator with afirst mating member formed at the distal insertion end of the firstdilator so as to prevent free rotation of the second dilator around thefirst dilator through at least a portion of the advancement; dilatingbodily tissue with a distal insertion end of the second dilator; andaligning a distal terminus of the second dilator with a distal terminusof the first dilator such that the second dilator mechanicallydisengages from the first mating member so as to enable free rotation ofthe second dilator around the first dilator.
 22. A method for dilatingbodily tissue as recited in claim 21, further comprising advancing athird dilator over the second dilator and the first dilator.
 23. Adilation system as recited in claim 16, wherein the first mating membercomprises at least one thread, and wherein the second mating member isformed at the distal insertion end of the second tubular body.